Related Party Transactions - Related Party Transactions Included in Consolidated Statements of Income (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Total financing revenues:
Manufacturers’ subvention and other revenues									$ 1,602	$ 1,374	$ 1,315
Interest expense:
Credit support fees incurred									94	92	91
Interest and other expenses									1	3	4
Insurance earned premiums and contract revenues:
Insurance premiums and contract revenues	$ 225	$ 220	$ 221	$ 216	$ 210	$ 202	$ 199	$ 193	882	804	719
Investment and other income, net:
Gain on sale of commercial finance business									0	0	197
Expenses:
Operating and administrative	$ 384	$ 323	$ 337	$ 313	$ 356	$ 325	$ 317	$ 279	1,357	1,277	1,161
TMCC-affiliated companies [Member]
Insurance earned premiums and contract revenues:
Insurance premiums and contract revenues									182	149	132
Investment and other income, net:
Interest and other income									13	9	8
Expenses:
Operating and administrative									80	73	81
Insurance losses and loss adjustment expenses									$ (3)	$ 0	$ 0